Selective implementation of barrier layers to achieve threshold voltage control in CMOS device fabrication with high-k dielectrics

ABSTRACT

The present invention provides a semiconductor structure including a semiconductor substrate having a plurality of source and drain diffusion regions located therein, each pair of source and drain diffusion regions are separated by a device channel. The structure further includes a first gate stack of pFET device located on top of some of the device channels, the first gate stack including a high-k gate dielectric, an insulating interlayer abutting the gate dielectric and a fully silicided metal gate electrode abutting the insulating interlayer, the insulating interlayer includes an insulating metal nitride that stabilizes threshold voltage and flatband voltage of the p-FET device to a targeted value and is one of aluminum oxynitride, boron nitride, boron oxynitride, gallium nitride, gallium oxynitride, indium nitride and indium oxynitride. A second gate stack of an nFET devices is located on top remaining device channels, the second gate stack including a high-k gate dielectric and a fully silicided gate electrode located directly atop the high-k gate dielectric.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/355,368, filed Jan. 16, 2009, which is a divisional of U.S. patentapplication Ser. No. 10/957,342, now filed Oct. 1, 2004, now U.S. Pat.No. 7,479,683 issued Jan. 20, 2009, which is a continuation-in-part ofU.S. patent application Ser. No. 10/863,830 entitled “SELECTIVEIMPLEMENTATION OF BARRIER LAYERS TO ACHIEVE THRESHOLD VOLTAGE CONTROL INCMOS DEVICE FABRICATION WITH HIGH-k DIELECTRICS”, filed Jun. 4, 2004,now U.S. Pat. No. 7,105,889, issued Sep. 12, 2006, the entire contentand subject matter of which is incorporated herein by reference. Thisapplication is also related to commonly owned and U.S. patentapplication Ser. No. 10/890,753 entitled “FORMATION OF FULLY SILICIDEDMETAL GATE USING DUAL SELF-ALIGNED SILICIDE PROCESS”, filed Jul. 14,2004, now U.S. Pat. No. 7,271,455, and commonly owned and U.S. patentapplication Ser. No. 10/845,719 entitled “A THRESHOLD AND FLATBANDVOLTAGE STABILIZATION LAYER FOR FIELD EFFECT TRANSISTORS WITH HIGHPERMITTIVITY GATE OXIDES”, filed May 14, 2004, now U.S. PatentApplication Publication No. 2005/0258491, the entire contents andsubject matter of which are incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to a semiconductor device, andmore particularly to a complementary metal oxide semiconductor (CMOS)structure that includes an interlayer between a fully silicided metalgate electrode and a high-k gate dielectric. The interlayer of thepresent invention is capable of stabilizing the threshold voltage(V_(t)) and flatband voltage (V_(fb)) of the structure. The presentinvention also relates to a complementary metal oxide semiconductor(CMOS) structure having nFET and pFET device regions, which structureincorporates an insulating interlayer between a fully silicided metalgate electrode and a high-k gate dielectric in at least one pFET deviceof the pFET device region, without incorporating the insulatinginterlayer into the nFET device region, wherein the insulatinginterlayer stabilizes the threshold voltage (V_(t)) and flatband voltage(V_(fb)) of the pFET devices without substantially impacting thethreshold voltage (V_(t)) and flatband voltage (V_(fb)) of the deviceswithin the nFET device region.

BACKGROUND OF THE INVENTION

Throughout the prior art, metal gate integration has proven difficult toachieve in a conventional process flow for metal oxide semiconductor(MOS) transistors. Most metal gate materials interact with the gatedielectric during the high temperature processing needed forsource/drain junction activation anneals. The need to keep the metalgate stack from receiving high temperature anneals has lead to thedevelopment of the “gate last” or “replacement gate” process for whichthe gate stack is fabricated last and remains below 500° C. duringsubsequent processing. Although the prior art replacement gate processincreases the number of material choices for a metal gate, the processincreases complexity and cost.

U.S. application Ser. No. 10/300,165, entitled “METHOD AND PROCESS TOMAKE MULTIPLE-THRESHOLD METAL GATE CMOS TECHNOLOGY”, filed Nov. 20,2002, now U.S. Pat. No. 6,846,734, describes an approach for forming ametal gate silicide in a conventional CMOS transistor processing flow,in which the “replacement gate” process is not used. In this approach,the number of processing steps has been minimized, therefore keeping thecomplexity to a minimum and cost down. A second advantage of thisapproach is the ability to deposit metal using standard physical vapordeposition for forming the silicide metal gate. Since the metal is notbeing directly deposited on the gate dielectric there is no need forchemical vapor deposition (CVD) or atomic layer deposition (ALD), whichreduces gate dielectric damage by eliminating the use of a plasma. Anadditional advantage is the ease of passivation of the gate dielectricafter silicide metal gate formation. Hydrogen readily diffuses throughthe silicide allowing passivation in a conventional furnace annealprocess.

Current CMOS technology uses silicides as contacts to source/drain andgate regions of the devices. Examples of silicides with low resistivityand contact resistance that are currently being used are the C54 phaseof TiSi₂, CoSi₂, and NiSi. All three of these silicides are integratedusing a self-aligned silicide process (i.e., a salicide process). Thisprocess consists of a blanket deposition of the metal (Ti, Co, or Ni)with a cap layer (such as TiN, Ti or W), annealing at a firsttemperature to form a first silicide phase (i.e., the C49 phase ofTiSi₂, CoSi, or NiSi), selectively wet etching the cap layer andunreacted metal that is not in contact with silicon, and annealing at asecond temperature to form the low resistant metal silicide phase (theC54 phase of TiSi₂ or CoSi₂). For low resistance NiSi, the second annealis not needed. An additional approach for the Ni silicide is to form ametal rich Ni silicide during the first anneal followed by the formationof NiSi during the second anneal. The advantage of these particularsilicides is that they all may be implemented with the self-alignedprocess avoiding additional lithographic steps.

In future technology, silicon dioxide or silicon oxynitride dielectricswill be replaced with a gate material that has a higher dielectricconstant. These materials are known as “high-k” materials with the term“high-k” denoting an insulating materials whose dielectric constant isgreater than 4.0, preferably greater than about 7.0. The dielectricconstants mentioned herein are relative to a vacuum unless otherwisespecified. Of the various possibilities, hafnium oxide, hafniumsilicate, or hafnium silicon oxynitride are particularly interesting assuitable replacement candidates for conventional gate dielectrics due totheir excellent thermal stability at high temperature. The higherdielectric constants allow for thicker dielectric films and thus lowergate leakage currents.

The combination of a fully silicided metal gate electrodes and a high-kgate dielectric is very attractive. Fully silicided metal gateelectrodes substantially eliminate the polycrystalline depletion effectand therefore result in a substantial decrease in the electricalthickness of the gate dielectric by approximately 0.4 nm to 0.7 nm.High-k dielectric materials allow for thicker gate dielectrics thanconventional gate dielectric materials and therefore decrease deviceleakage current by orders of magnitude in comparison to devicesincorporating conventional gate dielectric materials, such as SiO₂ andSiO_(x)N_(y). The combined benefits provide a gate stack that lowers theFETs power use (need to efficiently cool is lessened) and boosts theperformance.

Unfortunately, a gate stack comprising a fully silicided metal gateelectrode and a high-k gate dielectric, similar to a gate stackcomprising a polycrystalline Si gate conductor and a high-k gatedielectric disadvantageously suffers from pinning of the turn onvoltage, hereafter referred to as threshold voltage (V_(t)), for p-typefield effect transistors (pFETs). The terms “pinning of the turn onvoltage” denote a shift in the threshold voltage (V_(t)) of the deviceresulting from interaction between the high-k gate dielectric, such ashafnium oxide, with the gate conductor. The effect of the high-k gatedielectric on the threshold voltage (V_(t)) of semiconducting devices isnow discussed in greater detail.

In standard silicon CMOS technology, pFETs use a boron (or otheracceptor) doped p-type polysilicon layer as a gate electrode that isdeposited on top of a silicon dioxide or silicon oxynitride gatedielectric layer. The gate voltage is applied through the polysiliconlayer to create an inversion channel in the n-type silicon underneaththe gate dielectric layer. For a pFET to work properly, the inversionshould begin occurring at slightly negative voltages applied to thepolysilicon gate electrode. The poly-Si/gate dielectric/n-type siliconstack forms a capacitor that swings into inversion at around 0 V andinto accumulation around +1 V (depending on the substrate doping). Thethreshold voltage (V_(t)), which can be interpreted as the voltage atwhich the inversion starts occurring, is therefore approximately 0 V andthe flatband voltage (V_(fb)), which is the voltage just beyond whichthe capacitor starts to swing into accumulation, is approximately +1 V.The exact values of the threshold and flatband voltages (V_(t), V_(fb))have a dependence on the doping level in the silicon substrate, and canbe varied somewhat by choosing an appropriate substrate doping level.

Unfortunately, when pFETs are fabricated using high-k dielectrics, suchas hafnium oxide or hafnium silicate, it is a well known problem thatthe flatband voltage (V_(fb)) of the device is shifted from its idealposition of close to about +1 V, to about 0+/−300 mV. This shift inflatband voltage (V_(fb)) is published in C. Hobbs et al., entitled“Fermi Level Pinning at the Poly-Si/Metal Oxide Interface”, 2003Symposium on VLSI Technology Digest of Technical Papers. Consequently,the threshold voltage (V_(t)) of the device is shifted to approximately−1 V. This threshold voltage (V_(t)) shift is believed to be aconsequence of an intimate interaction between the Hf-based gatedielectric layer and the polysilicon layer. The threshold voltage(V_(t)) therefore is not in the “right” place, i.e., it is too high fora useable CMOS technology.

For a fully silicided metal gate and since polysilicon is deposited onthe high-k dielectric (hafnium oxide or hafnium silicate) at elevatedtemperatures (>600° C.), the same threshold pinning/shifting effect isoperable independent of silicide formation. FIG. 1 depicts a plot ofcapacitance v. voltage for pFET devices having a fully silicide NiSigate electrode on a SiO_(x)N_(y) gate dielectric, indicated by referencenumber 50, and pFET devices having a fully silicided NiSi gate electrodeon a HfO₂ high-k gate dielectric, indicated by reference number 55. Incomparison to pFET devices comprising a SiO_(x)N_(y) gate dielectric andfully silicided NiSi gate electrode, the threshold voltage (V_(t)) ofpFET devices comprising a HfO₂ high-k gate dielectric and a fullysilicided NiSi gate electrode is shifted approximately 230 mV. The pFETsdepicted in FIG. 1 have a gate dielectric thickness on the order ofabout 30 nm, a doping concentration of about 1E16 cm⁻² to about 5E17cm⁻², and a channel length on the order of about 50 μm.

One possible solution to the above problem of threshold voltage (V_(t))shifting is by substrate engineering in which channel implants can beused to shift thresholds. Although substrate engineering is one possiblemeans to stabilize threshold voltage (V_(t)) shift, it can do so to alimited extent, which is inadequate for FETs that include a gate stackcomprising a silicide metal gate electrode and a hafnium-containinghigh-k gate dielectric.

In view of the above mentioned problem in threshold voltage (V_(t)) andflatband voltage shift (V_(fb)), it has been nearly impossible todevelop a fully silicided metal gate electrode/high-k gate dielectricCMOS technology that is capable of stabilizing the threshold andflatband voltage (V_(t), V_(fb)) for FETs. As such, a method andstructure that is capable of stabilizing the threshold voltage (V_(t))and flatband voltage (V_(fb)) of FETs containing a fully silicided metalgate electrode/high-k dielectric gate stack is needed.

SUMMARY OF THE INVENTION

The present invention relates to a semiconducting structure having anadvanced gate stack including a fully silicided metal gate electrode, ahigh-k gate dielectric and an insulating interlayer that preventsintimate interaction between the fully silicided metal gate electrodeand the high-k gate dielectric, in which the insulating interlayerstabilizes the threshold voltage (V_(t)) of pFET devices. Specifically,the present invention provides a semiconducting device comprising asemiconductor substrate having a plurality of source and drain diffusionregions located therein, each of said source and drain diffusion regionsare separated by a device channel. A first gate stack of a pFET deviceis located on top of some of the device channels. The first gate stackincludes a high-k gate dielectric, an insulating interlayer abutting thegate dielectric and a fully silicided metal gate electrode abutting theinsulating interlayer. A second gate stack of an nFET device is locatedon top remaining device channels. The second gate stack included ahigh-k gate dielectric and a fully silicided gate electrode locateddirectly atop the high-k gate dielectric.

In accordance with the present invention, the source and drain diffusionregions can have a silicided surface, wherein the thickness of thesilicided portion of the source and drain diffusion regions is less thanthe thickness of the fully silicided metal gate electrode. The fullysilicided gate electrode and the silicided portions of the source anddrain diffusion regions can be composed of the same or different metalsilicide such as, for example, silicides of Ti, Ta, W, Co, Ni, Pt, Pdand alloys thereof. In a highly preferred embodiment of the presentinvention, the source and drain diffusion regions include CoSi₂, whilethe silicided metal gate includes NiSi or NiPtSi. The high-k gatedielectric comprises HfO₂, ZrO₂, Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃,Y₂O₃, SiO₂, nitrided SiO₂ or silicates, nitrides or nitrided silicatesthereof and has a dielectric constant greater than 4.0.

The insulating interlayer of the present invention comprises aninsulating metal nitride, which optionally comprises oxygen andtypically has a thickness ranging from about 1 Å to about 25 Å. Examplesof the insulating interlayer include aluminum nitride (AlN), aluminumoxynitride (AlO_(x)N_(y)), boron nitride (BN), boron oxynitride(BO_(x)N_(y)), gallium nitride (GaN), gallium oxynitride (GaON), indiumnitride (InN), indium oxynitride (InON) or combinations thereof. It isnoted that the insulating interlayer prevents intimate interactionbetween the fully silicided metal gate electrode and the high-k gatedielectric. Therefore, the insulating interlayer substantiallyeliminates the threshold voltage (V_(t)) shift typically present in pFETdevices having high-k gate dielectrics and gate structures in which theinsulating interlayer is not present.

In addition to the structure described above, the present invention alsoprovides a complementary metal oxide semiconductor (CMOS) structurecomprising nFET devices and pFET devices comprising fully silicidedmetal gates and high-k gate dielectrics, in which an insulatinginterlayer incorporated into the gate stack of the pFET devicesstabilizes the threshold voltage (V_(t)) of the pFET device, withoutadversely affecting the threshold voltage (V_(t)) of the nFET devices.Applicants have determined that the presence of the insulatinginterlayer, such as AlN, between a fully silicided metal gate conductorand a high-k dielectric in nFET devices disadvantageously results in apositive threshold voltage (V_(t)) shift. The positive shift in thethreshold voltage (V_(t)) due to the incorporation of the AlN insulatinginterlayer within the nFET device is an equally unfavorablecharacteristic as the original negative shift in the threshold voltage(V_(t)) of the pFET device, without the AN insulating interlayer.Applicants have discovered that by removing the AlN layer from nFETdevices, the positive shift in threshold voltage (V_(t)) can beeliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot showing the capacitance-voltage curves for nFETdevices. The capacitance voltage curves include plots for an nFETcomprising a fully silicided NiSi gate on a HfO₂ high-k dielectric layerand an nFET comprising a fully silicided NiSi gate on a SiO_(x)N_(y)gate dielectric.

FIG. 2( a) is a pictorial representation (through a cross sectionalview) of one embodiment of the inventive semiconducting device thatincludes a pFET device region having a threshold voltage (V_(t))stabilizing insulating interlayer between a high-k gate dielectric and afully silicided metal gate electrode.

FIG. 2( b) is a pictorial representation (through a cross sectionalview) of another embodiment of the inventive semiconducting device thatincludes a pFET device region having a threshold voltage (V_(t))stabilizing insulating interlayer between a high-k gate dielectric and afully silicide metal gate electrode and an nFET device region from whichthe insulating interlayer has been removed using the selective etchprocess of the present invention.

FIGS. 3-7 are pictorial representations (through cross sectional views)illustrating the process steps for providing the inventivesemiconducting devices depicted in FIGS. 2( a) and 2(b).

FIG. 8 is a plot depicting AlN deposition time v. flatband voltage(V_(fb)), in which data points were provided for transistor comprising aHfO₂ high-k gate dielectric without an AlN insulating interlayer, atransistor comprising a HfO₂ high-k gate dielectric with an AlNinsulating interlayer, a transistor comprising an AlN gate dielectric,and a transister comprising a SiO₂ gate dielectric.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a semiconducting device thatincludes an insulating interlayer between a fully silicided gateelectrode and a high-k gate dielectric, wherein the insulatinginterlayer is capable of stabilizing the threshold voltage (V_(t)) andflatband voltage (V_(fb)) of the structure will now be described in moredetail. The term “high-k gate dielectric” denotes a dielectric materialhaving a dielectric constant of 4 or greater.

In the accompanying drawings, which are not drawn to scale, like and/orcorresponding elements are referred to by like reference numerals. It isnoted that in the drawings two MOS device regions are shown to be formedatop a single semiconductor substrate. Although illustration is made tosuch an embodiment, the present invention is not limited to theformation of any specific number of MOS devices on the surface of thesemiconductor structure. Instead, the method of the present inventionforms at least one fully silicided MOS device on a surface of asemiconductor substrate.

Reference is made to FIG. 2( a), which is a pictorial representation(through a cross sectional view) showing one embodiment of thesemiconducting device 10 of the present invention. Specifically, thesemiconducting device 10 includes a semiconductor substrate 12, sourceand drain diffusion regions 14 located in the semiconductor substrate12, which are separated from each other by device channel 16, and a gatestack 1 comprising a high-k dielectric 20 located atop the devicechannel 16, an insulating interlayer 22 located atop the high-kdielectric 20 and a fully silicided metal gate electrode 30 located atopthe insulating interlayer 22. The insulating interlayer 22 preventsinteraction between the high-k dielectric 20 and the fully silicidedgate electrode 30, therefore stabilizing the threshold voltage (V_(t))in pFET devices. The semiconducting device further comprises silicidedsource drain contacts 26. Spacers 6 are also present abutting thesidewalls of the fully silicided metal gate electrode 30.

In another embodiment of the semiconducting device of the presentinvention, a CMOS device such as depicted in FIG. 2( b) is provided. Inthe drawings, the insulating interlayer 22 is removed from the deviceswithin the nFET device region 25 of the substrate 12 and remains withinthe devices of the pFET device region 15, wherein the remaining portionof the insulating interlayer 22 stabilizes the threshold voltage (V_(t))and the flatband voltage (V_(fb)) of the pFET devices without degradingthe stability of the threshold voltage (V_(t)) and flatband voltage(V_(fb)) of the nFET devices.

The various components of the structures shown in FIGS. 2( a) and 2(b)as well as the process that can be used in forming the same will now bedescribed in greater detail referring to FIGS. 3-7.

Referring to FIG. 3, an initial layered stack 5 is first providedcomprising blanket layers of the high-k gate dielectric 20 andinsulating interlayer 22 on a surface of the semiconductor substrate 12.In accordance with the present invention, the high-k gate dielectric 20is located between the insulating interlayer 22 and the semiconductorsubstrate 12. In some instances an additional dielectric layer can belocated between the high-k material and the semiconductor substrate.This layer can be a silicon oxide or a silicon oxynitride.

The semiconductor substrate 12 employed in the present inventioncomprises any semiconducting material including, but not limited to: Si,Ge, SiGe, SiC, SiGeC, Ga, GaAs, InAs, InP and all other III/V or II/VIcompound semiconductors. Semiconductor substrate 12 may also comprise anorganic semiconductor or a layered semiconductor such as Si/SiGe, asilicon-on-insulator (SOI) or a SiGe-on-insulator (SGOI). In someembodiments of the present invention, it is preferred that thesemiconductor substrate 12 be composed of a Si-containing semiconductormaterial, i.e., a semiconductor material that includes silicon. Thesemiconductor substrate 12 may be doped, undoped or contain doped andundoped regions therein.

The semiconductor substrate 12 may also include a first doped (n- or p-)region, and a second doped (n- or p-) region. For clarity, the dopedregions are not specifically shown in the drawing of the presentapplication. The first doped region and the second doped region may bethe same, or they may have different conductivities and/or dopingconcentrations. These doped regions are known as “wells”.

At least one isolation region 31 is typically formed into thesemiconductor substrate 12. The isolation region 31 may be a trenchisolation region or a field oxide isolation region. The trench isolationregion is formed utilizing a conventional trench isolation process wellknown to those skilled in the art. For example, lithography, etching andfilling of the trench with a trench dielectric may be used in formingthe trench isolation region. Optionally, a liner may be formed in thetrench prior to trench fill, a densification step may be performed afterthe trench fill and a planarization process may follow the trench fillas well. The field oxide may be formed utilizing a so-called localoxidation of silicon process. Note that the at least one isolationregion 31 provides isolation between neighboring gate regions, typicallyrequired when the neighboring gates have opposite conductivities. Theneighboring gate regions can have the same conductivity (i.e., both n-or p-type), or alternatively they can have different conductivities(i.e., one n-type and the other p-type).

After forming the at least one isolation region 31 within thesemiconductor substrate 12, a high-k gate dielectric 20 is formed on asurface of the structure. The high-k gate dielectric 20 can be formed bya thermal growth process such as, for example, oxidation, nitridation oroxynitridation. Alternatively, the high-k gate dielectric 20 can beformed by a deposition process such as, for example, chemical vapordeposition (CVD), plasma-assisted CVD, metal organic chemical vapordeposition (MOCVD), atomic layer deposition (ALD), evaporation, reactivesputtering, chemical solution deposition and other like depositionprocesses. The high-k gate dielectric 20 may also be formed utilizingany combination of the above processes.

The high-k gate dielectric 20 is comprised of an insulating materialhaving a dielectric constant of greater than about 4.0, preferablygreater than 7.0. Specifically, the high-k gate dielectric 20 employedin the present invention includes, but not limited to: an oxide,nitride, oxynitride and/or silicate including metal silicates andnitrided metal silicates. In one embodiment, it is preferred that thegate dielectric 20 is comprised of an oxide such as, for example, HfO₂,ZrO₂, Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃, Y₂O₃ and mixtures thereof.Highly preferred examples of the gate dielectrics 20 include HfO₂,hafnium silicate and hafnium silicon oxynitride.

The physical thickness of the high-k gate dielectric 20 may vary, buttypically, the high-k gate dielectric 20 has a thickness from about 0.5to about 10 nm, with a thickness from about 0.5 to about 3 nm being moretypical. It may be deposited above a thin (on the order of about 0.1 toabout 1.5 nm) layer of silicon oxide or silicon oxynitride that is firstdeposited on the substrate.

Next, insulating interlayer 22 is formed atop the blanket layer ofhigh-k gate dielectric 20. As stated above, the insulating interlayer 22employed in the present invention has at least one of the followingcharacteristics: (i) it is capable of preventing interaction between thehigh-k gate dielectric 20 and the subsequently formed fully silicidedmetal gate electrode 30 by spatial separation; (ii) it has asufficiently high dielectric constant (on the order of about 4.0 orgreater) such that there is a minimal decrease in gate capacitance (dueto series capacitance effect) because of its addition; (iii) it maydissociate, at least partially, to provide a supply of p-type dopants inthe near interfacial layer to ensure p-type behavior of the nearinterfacial Si-containing gate electrode material; (iv) it can preventoutdiffusion of atoms from the high-k gate dielectric 20 into the fullysilicided metal gate electrode 30; and (v) it can prevent lateroxidation under the fully silicided metal electrode 30.

The insulating interlayer 22 of the present invention is a chemicalinterlayer that prevents interaction between the high-k gate dielectric20 and the fully silicided metal electrode 30 to be subsequently formed.The insulating interlayer 22 of the present invention is substantiallynon-reactive (there may be slight or partial decomposition, such as whenits acts as a dopant source) with the underlying high-k gate dielectric20, therefore it does not react with the high-k gate dielectric 20.Another characteristic feature of the inventive insulating interlayer 22is that silicon cannot reduce the inventive insulating interlayer 22. Incases in which some dissociation of the inventive insulating interlayer22 may occur, the inventive insulating interlayer 22 should be either ap-type dopant or a neutral dopant so that device performance is notadversely affected. Also, the insulating interlayer 22 employed in thepresent invention should be a refractory compound that is able towithstand high temperatures (of approximately 1000° C., typical ofstandard CMOS processing).

Insulating materials that fit the above-mentioned criteria and are thusemployed as the insulating interlayer 22 of the present inventioninclude any insulating metal nitride that may optional include oxygentherein. Examples of insulating interlayers include, but are not limitedto: aluminum nitride (AlN), aluminum oxynitride (AlO_(x)N_(y)), boronnitride (BN), boron oxynitride (BO_(x)N_(y)), gallium nitride (GaN),gallium oxynitride (GaON), indium nitride (InN), indium oxynitride(InON) and combinations thereof. In one preferred embodiment of thepresent invention, the insulating interlayer 22 is AlN or AlO_(x)N_(y).

The insulating interlayer 22 is a thin layer that typically has athickness from about 1 to about 25 Å, with a thickness from about 2 toabout 15 Å being more typical. The insulating interlayer 22 can beformed by various deposition processes such as, for example, chemicalvapor deposition (CVD), plasma-assisted CVD, atomic layer deposition(ALD) using aluminum and nitrogen-based precursors, physical vapordeposition or molecular beam deposition where the metal is evaporatedalong with a beam or ambient of atomic or molecular nitrogen (that maybe optionally an excited species) and optionally oxygen, metalorganicchemical vapor deposition (MOCVD), atomic layer deposition, sputtering,and the like. Alternatively, the insulating interlayer 22 can be formedby thermal nitridation or oxynitridation of a previously depositedinsulating metal layer. Alternatively, the oxynitride of the metal maybe created by first depositing the metal nitride, followed by partialoxidation in a suitable oxygen environment to create and oxynitride.

One preferred method of forming the interlayer insulating layer 22 is byevaporating, under a high vacuum, Al from a standard Al effusion cellthat is resistively heated, and using a nitrogen, or oxygen and nitrogenbeams from commercial radio frequency (RF) atomic nitrogen or nitrogenand oxygen sources. For deposition of the nitride alone, a single RFnitrogen source suffices. For the oxynitride, a second RF source ofoxygen may be used. Alternatively, the oxygen may be delivered simply asa molecular beam without an RF source. The process of evaporating undera high vacuum is described, for example, in U.S. Pat. No. 6,541,079, theentire content of which is incorporated herein by reference. Theeffusion cell typically has a temperature from about 1000° C.-1200° C.during the evaporation process. The evaporation process is typicallyperformed using a RF source having a power from about 200-450 W and aflow rate from about 1-3 sccm. These numbers can also be widely variedfrom the stated bounds without problems. The substrate temperature istypically kept between 150° C. to 650° C. during deposition. Again, thedeposition temperature can also be varied outside the stated ranges.Base vacuum chamber pressure is typically about 5×10⁻¹⁰ to 2×10⁻⁹ torr.

Notwithstanding the technique employed in forming the same, theinsulating interlayer 22 formed in the present invention is a continuousand uniform layer that is present atop the high-k gate dielectric 20. By“continuous”, it is meant that the insulating interlayer 22 contains nosubstantial breaks and/or voids therein; by “uniform” it is meant thatthe insulating interlayer 22 has nearly the same, as deposited,thickness across the structure. The insulating interlayer 22 may beamorphous meaning that it can lack a specific crystal structure. Theinsulating interlayer 22 may exist in other phases besides amorphousdepending on the material used as well as the technique that is used informing the same.

In one embodiment of the present invention, the insulating interlayer 22can be removed from the portion of the substrate in which nFETs aresubsequently provided, wherein the remaining portion of the insulatinginterlayer 22 stabilizes the threshold voltage (V_(t)) of in pFETdevices, without degrading the performance characteristics of the nFETdevices. Alternatively, the insulating interlayer 22 may be positionedin both nFET and pFET devices. The embodiment of the present inventionwherein the insulating interlayer 22 is removed from the portion of thesubstrate 12 in which nFETs are subsequently produced is now describedwith reference to FIG. 3( b).

First, a block mask 50 is formed protecting the portion of the substrate12 in which pFETs are subsequently formed. This portion of the substrateis hereafter referred to as the pFET device region 15. The exposedportion of the substrate that is not protected by the block mask 50 issubsequently processed to provide nFET devices and is hereafter referredto as the nFET device region 25.

The block mask 50 may comprise conventional soft and/or hardmaskmaterials and can be formed using deposition, photolithography andetching. In a preferred embodiment, the block mask 50 comprises aphotoresist. A photoresist block mask 50 can be produced by applying aphotoresist layer to the substrate 12 surface, exposing the photoresistlayer to a pattern of radiation, and then developing the pattern intothe photoresist layer utilizing conventional resist developer.

Alternatively, the block mask 50 can be a hardmask material. Hardmaskmaterials include dielectric systems that may be deposited by chemicalvapor deposition (CVD) and related methods. Typically, the hardmaskcomposition includes silicon oxides, silicon carbides, silicon nitrides,silicon carbonitrides, etc. Spin-on dielectrics may also be utilized asa hardmask material including, but not limited to: silsequioxanes,siloxanes, and boron phosphate silicate glass (BPSG). A block mask 50comprising a hardmask material may be formed by blanket depositing alayer of hardmask material; providing a patterned photoresist atop thelayer of hardmask material; and then etching the layer of hardmaskmaterial to provide a block mask 50 protecting the pFET device region15, in which etching comprises an etch chemistry having a highselectivity to the patterned photoresist and the surface of the nFETdevice region 25.

Still referring to FIG. 3( b), in a next process step the exposedportion of the insulating interlayer 22 is removed from the nFET deviceregion 25 using a highly selective etch process. This highly selectiveetch preferably comprises an etch chemistry which removes the exposedportion of the insulating interlayer 22 from the nFET device region 25,without substantially etching the underlying high-k dielectric 20 or theblock mask 50 that protects the pFET device region 15. In a preferredembodiment, this etch chemistry removes the AN insulating interlayer 22,without substantially etching an underlying HfO₂ high-k dielectric 20.

In a preferred embodiment of the present invention, the wet etchchemistry comprises a solution of HCl and peroxide, the preferredconcentration being 3:1 HCl:H₂O₂. In addition to HCl/peroxide solutions,it is proposed that other inorganic acids and oxidizing agents canproduce the same results so long as the etch chemistry does not attackthe high-k gate dielectric 20. The oxidizing agents may includeperoxides, nitrates, nitrites, perchlorates, chlorates, chlorites,hypochlorites, dichromates, permanganates, persulfates or combinationsthereof. The inorganic acids can include sulfuric acid, phosphoric acidor combinations thereof. Etch rate may be impacted by the pH of the etchchemistry. The pH of the etch chemistry may range from about 1 to about8, preferably ranging from about 2 to about 6, most preferably beingabout 2.8. The etch composition can be mixed during an exothermicreaction. The wet etch may be conducted in an oxygen-containingenvironment and may be conducted at room temperature or at an elevatedtemperature. Preferably, the etch temperature is 15° C. to 80° C.Following this etching step, the block mask 50 is removed using achemical strip and the substrate 12 is rinsed with deionized water anddried in a N₂ ambient.

Referring to FIG. 4, in a next process step, a blanket layer ofpolysilicon 19 (i.e., polycrystalline silicon) which becomes the fullysilicided metal gate electrode 30 is formed atop the pFET device region15 and the nFET device region 25 of the substrate 12 utilizing a knowndeposition process such as, for example, physical vapor deposition, CVDor evaporation. FIG. 4 depicts the embodiment of the present inventionin which the insulating interlayer 22 is removed from the nFET deviceregion 25, wherein the blanket layer of polysilicon 19 is depositeddirectly atop the high-k dielectric 20 in the nFET device region 25 anddirectly atop the insulating interlayer 22 in the pFET device region 15.

It is noted that FIGS. 4-7 depict the processing steps for providing theinventive structure depicted in FIG. 2( b). Although not depicted inFIGS. 4-7, the insulating interlayer 22 can be present in both the nFETand pFET device regions 15, 25, wherein the blanket layer of polysilicon19 is deposited directly atop the insulating interlayer 22 in both thenFET and pFET device regions 15, 25. Therefore, the processing stepsdepicted in FIGS. 4-7 are applicable for providing the inventivestructure depicted in FIG. 2( a), in which the insulating interlayer hasnot been removed from the nFET device region 25.

The blanket layer of polysilicon 19 may be doped or undoped. If doped,an in-situ doping deposition process may be employed in forming thesame. Alternatively, a doped polysilicon layer 19 can be formed bydeposition, ion implantation and annealing. The doping of thepolysilicon layer 19 will shift the workfunction of the silicided metalgate formed. Illustrative examples of dopant ions include As, P, B, Sb,Bi, In, Al, Ga, Tl or mixtures thereof.

Preferable doses for the ion implants are 1E14 (=1×10¹⁴) to 1E16(=1×10¹⁶) atoms/cm² or more preferably 1E15 to 5E15 atoms/cm². Thethickness, i.e., height, of the polysilicon layer 19 deposited at thispoint of the present invention may vary depending on the depositionprocess employed. Typically, the polysilicon layer 19 has a verticalthickness from about 20 to about 180 nm, with a thickness from about 40to about 150 nm being more typical.

After deposition of the blanket layer of polysilicon 19, a dielectriccap layer 17 is formed atop the blanket layer of polysilicon 19utilizing a deposition process such as, for example, physical vapordeposition or chemical vapor deposition. The dielectric cap layer 17 maybe an oxide, nitride, oxynitride or any combination thereof. In oneembodiment, a nitride such as, for example, Si₃N₄, is employed as thedielectric cap layer 17. In yet another embodiment, the dielectric caplayer 17 is an oxide such as SiO₂. The thickness, i.e., height, of thedielectric cap layer 17 is from about 20 to about 180 nm, with athickness from about 30 to about 140 nm being more typical.

In one embodiment, the blanket layer of polysilicon 19 and dielectriccap layer 17 have a total height that ranges from about 50 to about 180nm. In yet another embodiment, the height of the blanket polysiliconlayer 19 and the dielectric cap layer 17 is about 120 nm; typically 70nm polysilicon and 50 nm dielectric cap 17.

Referring to FIG. 5, the blanket polysilicon layer 19 and dielectric caplayer 17 are then patterned by lithography and etched so as to providepatterned gate stacks 18. The patterned gate stacks 18 may have the samedimension, i.e., length, or they can have variable dimensions to improvedevice performance. Each patterned gate stack 18 at this point of thepresent invention includes a polysilicon gate 24 (note polysilicon gate24 comprises polySi layer 19) and dielectric cap 17. The lithographystep includes applying a photoresist to the upper surface of thedielectric cap layer 17, exposing the photoresist to a desired patternof radiation and developing the exposed photoresist utilizing aconventional resist developer. The pattern in the photoresist is thentransferred to the dielectric cap layer 17 and the blanket layer ofpolysilicon 19 utilizing one or more dry etching steps. In someembodiments, the patterned photoresist may be removed after the patternhas been transferred into the dielectric cap layer 17. In otherembodiments, the patterned photoresist is removed after etching has beencompleted.

Suitable dry etching processes that can be used in the present inventionin forming the patterned gate stacks include, but are not limited to:reactive ion etching, ion beam etching, plasma etching or laserablation. The dry etching process employed is typically selective to theunderlying high-k gate dielectric 20 therefore this etching step doesnot typically remove the high-k gate dielectric 20. In some embodiments,this etching step may however be used to remove portions of the high-kgate dielectric 20 that are not protected by the gate stacks 18.

Next, at least one spacer 6 is formed on exposed sidewalls of eachpatterned gate stack 18. The at least one spacer 6 is comprised of aninsulator such as an oxide, nitride, oxynitride and/or any combinationthereof. The at least one spacer 6 is formed by deposition and etching.The width of the at least one spacer 6 must be sufficiently wide enoughsuch that the source and drain silicide contacts (to be subsequentlyformed) do not encroach underneath the edges of the gate stack 18.Typically, the source/drain silicide does not encroach underneath theedges of the gate stack when the at least one spacer has a width, asmeasured at the bottom, from about 15 to about 80 nm.

After spacer formation, source and drain diffusion regions 14 are formedinto the substrate 12. The source and drain diffusion regions 14 areformed utilizing ion implantation and an annealing step. The annealingstep serves to activate the dopants that were implanted by the previousimplant step. The conditions for the ion implantation and annealing arewell known to those skilled in the art.

Next, and if not previously removed, the exposed portion of the high-kgate dielectric 20 is removed utilizing a chemical etching process thatselectively removes the high-k gate dielectric 20. This etching stepstops on an upper surface of the semiconductor substrate 12 as well asan upper surface of the isolation regions 31. Although any chemicaletchant may be used in removing the exposed portions of the gatedielectric 20, in one embodiment dilute hydrofluoric acid (DHF) is used.

Source and drain silicide contacts 26 (see FIG. 6) are then formed usinga salicide process which includes the steps of depositing a silicidemetal on an exposed surface of the substrate 12 that includes the sourceand drain diffusion regions 14, optionally depositing an oxygendiffusion barrier material such as TiN on the silicide metal, firstannealing to form a silicide, selective etching any non-reacted metalincluding barrier material if used and, if needed, performing a secondannealing step. When the semiconductor substrate 12 does not comprisesilicon, a layer of silicon (not shown) can be grown atop the exposedsurface of the semiconductor substrate 12 and can be used in forming thesource and drain silicide contacts 26.

The silicide metal used in forming the source and drain silicidecontacts 26 comprises any metal that is capable of reacting with siliconto form a metal silicide. Examples of such metals include, but are notlimited to: Ti, Ta, W, Co, Ni, Pt, Pd and alloys thereof. In oneembodiment, Co is a preferred metal. In such an embodiment, the secondannealing step is required. In another embodiment, Ni or Pt ispreferred. In this embodiment, the second annealing step is typicallynot performed.

The metal used in forming the source/drain silicides 26 may be depositedusing any conventional deposition process including, for example,sputtering, chemical vapor deposition, evaporation, chemical solutiondeposition, plating and the like.

The first anneal is typically performed at lower temperatures than thesecond annealing step. Typically, the first annealing step, which may,or may not, form a high resistance silicide phase material, is performedat a temperature from about 300° to about 600° C. using a continuousheating regime or various ramp and soak heating cycles. More preferably,the first annealing step is performed at a temperature from about 350°to about 550° C. The second annealing step is performed at a temperaturefrom about 600° C. to about 800° C. using a continuous heating regime orvarious ramp and soak heating cycles. More preferably, the secondannealing step is performed at a temperature from about 650° C. to about750° C. The second anneal typically converts the high resistancesilicide into a silicide phase of lower resistance.

The salicide anneals are carried out in a gas atmosphere, e.g., He, Ar,N₂ or forming gas. The source and drain silicide contacts 26 annealingsteps may use different atmospheres or the annealing steps may becarried out in the same atmosphere. For example, He may be used in bothannealing steps, or He can be used in the first annealing step and aforming gas may be used in the second annealing step.

The source and drain silicide contacts 26, which are formed utilizingthe above-mentioned process, are self-aligned to the gate regions 18.Moreover, the silicided source and drain contacts 26 have a thickness(measured vertically) of less than 500 Å, with a thickness from about150 to about 300 Å being more typical. Note that 10 Å=1 nm.

Next, and as shown in FIG. 6, the dielectric cap layer 17 is removedfrom each gate region 18 so that the underlying polysilicon gateconductor 24 is exposed. During the removal of the dielectric cap 17from atop the polysilicon gate conductor 24, a surface portion of theisolation region 31 may also be removed so as to provide an isolationregion 31 having a recessed surface. The recessed surface is labeled as4 in FIG. 6. The amount of recessing is not critical to the presentinvention, but typically, the at least one isolation region 31 can berecessed from about 100 to about 500 Å below the upper surface of thesemiconductor substrate 12 during this step of the present invention.

The dielectric cap 17 is removed in the present invention by utilizingan etching process, wet or dry, which selectively removes the dielectriccap material from the structure. Although a dry etching process such asreactive-ion etching (RIE), ion beam etching (IBE), and plasma etchingcan be employed, it is preferred that a wet etch process be employed inselectively removing the dielectric cap 17 without removing much of thesilicided source and drain regions 26. An example of a wet etch processthat can be used to selectively remove the dielectric cap 17 includesdilute hydrofluoric acid (DHF) mixed with at least one additive whichselectively adsorbs at the silicided source and drain contacts 26, butnot at the dielectric cap 17. This selective adsorption of the additivesis achieved by exploiting the difference in the electro-kinetic behaviorof the silicided source and drain contacts 26 and the dielectric cap 17in the DHF solution. As the additives form a very thin adsorbed layer(˜2-5 nm) at the surface of silicided source and drain contacts 26, thatregion would experience almost negligible etch rate, whereas thedielectric surface 17 will be etched at rates similar to DHF onlysolutions. Also, instead of mixing the additives to the DHF solution,the same effect may also be realized by exposing the surfaces to anaqueous or inaqeous solutions with the above said additives and thenetching in DHF solution. Examples of additive that can be employedduring the selective etching process include, but are not limited to:any organic and inorganic compounds that would selectively adsorb at thesilicided surfaces 26 and not the dielectric cap 17, in general, and allamphoteric molecules such as surfactants and polymers in specific.

In some embodiments of the present invention, a protective cap layersuch as, for example, a silicon oxynitride layer (i.e., SiO_(x)N_(y))can be foamed over the silicided source and drain contacts 26. This steptypically is performed prior to removing the dielectric cap 17. Theprotective cap layer is used in the present invention to ensure that thesilicided source and drain contacts 26 do not undergo furthersilicidation with the silicide metal used in forming the fully silicidedgate electrode. The protective cap can be formed, for example, bysubjecting the SiO₂ layer atop the silicided source and drain contacts26 to a plasma of nitrogen. In addition to plasma nitrogen treatment,the silicided source and drain contacts 26 can be modified using otherwet or dry chemistries that are capable of forming a protective capthereon. If present, the protective cap is a thin layer whose thicknessis typically from about 0.5 to about 3 nm.

The protective cap can also be formed by ion implantation of a speciesthat can slow down, i.e., substantially hinder, silicide metaldiffusion. Nitrogen is one example of a species that can be ionimplanted. Another method of forming the protective cap is by depositinga silicide metal alloy atop the silicided source and drain contacts 26which will introduce an impurity to slow down silicide metal diffusion.The silicide metal alloy is defined hereinbelow.

After removing the cap dielectric 17 from atop the polysilicon gateconductor 24, a second salicide process is then performed to consume thepolysilicon conductor 24 forming fully silicided metal gate electrode30. The second salicide process is exemplified in FIGS. 7 and 8. Thefirst step of the second salicide process includes depositing a blanketsilicide metal 28 atop the structure shown in FIG. 6. The resultantstructure including the blanket silicide metal 28 is shown, for example,in FIG. 7. The silicide metal 28 can be deposited using one of thedeposition processes mentioned above in forming the metal used insilicide source and drain contact 26 formation. The silicide metal 28can be the same or different than the metal used in forming thesilicided source and drain contacts 26.

The silicide metal 28 can be composed of Ti, Hf, Ta, W, Co, Ni, Pt, Pdor alloys thereof. In one embodiment, the silicide metal 28 is Co; CoSi₂forms using a two step annealing process. In another embodiment of thepresent invention, the silicide metal 28 is Ni or Pt; NiSi and PtSiformed using a single annealing step.

The silicide metal 28 thickness is selected so as to form the silicidephase with the appropriate workfunction for the particular MOS deviceand to consume all of the polysilicon conductor. For example, NiSi has aworkfunction of 4.65 eV, and if the initial polysilicon height is 50 nm,the amount of Ni needed is about 27 nm. CoSi₂ has a workfunction of 4.45eV, and if the initial polysilicon height is 50 nm, the amount of Coneeded is about 14 nm. Although the silicide metal thicknesses given arethe amount necessary to just consume the polysilicon, it is preferred ifthe thickness were in excess by about 10% to make sure consumption iscomplete.

In some embodiments (not shown), an oxygen diffusion barrier, such asTiN or W, is formed atop the silicide metal 28.

After deposition of the silicide metal 28, a first anneal is employed toform a first silicide phase in the structure; the first silicide phasemay or may not represent the lowest resistivity phase of a metalsilicide. The first anneal is performed utilizing the ambients andtemperatures described above in forming the source/drain silicidecontacts 26. Next, a selective wet etch step is employed to remove anynon-reactive silicide metal from the structure.

For some metal silicides, the salicide process may be stopped at thispoint since the polysilicon is consumed and the resistivity of the firstsilicide phase is close to minimum values for the phase. This is in thecase for Ni and Pt. In other cases, for example when Co or Ti are usedas the silicide metal, a second higher temperature anneal (as describedabove) is needed for the consumption of the remaining polysilicon andforming a second silicide phase material. In this embodiment, the firstsilicide phase is a high resistivity phase silicide material, while thesecond silicide phase material is a lower resistivity phase silicidematerial.

The resultant structure including fully silicided metal gate electrode30 is depicted in FIG. 2( b). It is noted that the above-describedprocess is equally applicable to the structure depicted in FIG. 2( a),in which the insulating interlayer is present in both pFET and nFETdevices. The fully silicided metal gates 30 are located atop theinsulating interlayer 22 or gate dielectric 18 in an area previouslyoccupied by the polysilicon conductor 24.

As shown, the fully silicided metal gate 30 is thicker than thecorresponding silicided source and drain contacts 26. Typically, thesilicided source and drain contacts 26 have a thickness that is lessthan 500 Å, while the silicided metal gate 30 has a thickness that isgreater than 500 Å. In a preferred embodiment, the silicided source anddrain contacts 26 typically have a thickness that is less than 300 Å,while the fully silicided metal gate electrode 30 has a thickness thatis greater than 500 Å. In yet another preferred embodiment, thesilicided source and drain contacts 26 typically have a thickness thatis less than 200 Å, while the fully silicided metal gate electrode 30has a thickness that is greater than 500 Å.

In one preferred embodiment, the silicided source and drain contacts 26comprise CoSi₂ and the fully silicided metal gates 30 comprise NiSi orNiPtSi. In another embodiment, the fully silicided metal gates 30comprise NiGe or NiPtGe.

After completion of the inventive metal silicide gate processingmentioned above, the conventional approach for building a multilayerinterconnect structure for transistor to transistor and transistor toexternal contacts can be employed.

In the process of the present invention, the silicided metal used informing the silicided source and drain contacts and the silicided metalgate may include an alloying additive that can enhance the formation ofthe metal silicide. Examples of alloying additives that can be employedin the present invention include, but are not limited to: C, Al, Ti, V,Cr, Mn, Fe, Co, Ni, Cu, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta,W, Re, Ir, Pt or mixtures thereof, with the proviso that the alloyingadditive is not the same as the material used in forming the silicide.When present, the alloying additive is present in an amount from about0.1 to about 50 atomic percent. The alloying additive may be introducedas a dopant material to the silicide metal layer or it can be a layerthat is formed atop the silicide metal layer prior to annealing.

It should be noted that although the above describes an initialstructure that does not include raised source/drain regions, the presentinvention also contemplates the presence of raised source/drain regionsin the initial structure. The raised source/drain regions are formedutilizing conventional techniques well known to those skilled in theart. Specifically, the raised source/drain regions are formed bydepositing any Si-containing layer, such as epi Si, amorphous Si, SiGe,and the like, atop the substrate 12 prior to implanting.

As stated above the present invention provides a semiconductor structurecomprising a thick, fully silicided metal gate electrode and a thinsilicided source/drain regions abutting the fully silicided metal gateelectrode. In some embodiments of the present invention, thesemiconductor structure is characterized as having a silicide metalsurface layer atop the silicided source/drain regions that includes asmall amount (less than about 25 atomic %) of metal used in making thefully silicided gate, which does not form a further silicide atop thesilicided source/drain regions. The surface layer of metal silicide atopthe source/drain region has a thickness of about 10 nm or less. Thus,for example, it is possible to form a structure having a fully silicidedNiSi gate and contacts atop the source/drain regions that comprise CoSi₂with Ni as a surface layer.

The following examples are provided to further illustrate the presentinvention and demonstrate some advantages of incorporating the inventiveinsulating interlayer 22 between a fully silicided gate conductor and ahigh-k gate dielectric in an nFET device.

EXAMPLE

FIG. 8 depicts a plot of flatband voltage (V_(fb)) vs. AlN depositiontime, in which the plot depicts the effect of an AlN insulatinginterlayer positioned between a fully silicided NiSi metal gateelectrode and a HfO₂ high-k gate dielectric in pFET devices. The dataplotted was provided by test capacitors 90 comprising an AlN insulatinginterlayer between a fully silicided NiSi metal gate and a HfO₂ high-kgate dielectric; an AlN control 85 comprising a fully silicided NiSimetal gate electrode on an AlN insulating interlayer; a HfO₂ control 95comprising a fully silicided NiSi metal gate electrode on a HfO₂ high-kgate dielectric; and a SiO₂ control 80 comprising a fully silicided NiSimetal gate electrode on a SiO₂ gate dielectric. The flatband voltage(Vfb) data was provided from capacitance v. voltage curves measured fromthe above-described samples using electrical testing methods.

The test capacitors 90 comprising an AlN insulating interlayerpositioned between a fully silicided NiSi metal gate electrode and HfO₂high-k gate dielectric were provided by forming a HfO₂ high-k gatedielectric on a silicon substrate using metal organic chemical vapordeposition (MOCVD) and atomic layer chemical vapor deposition (ALCVD).The HfO₂ high-k gate dielectric had a thickness in the range of about 2nm to about 4 nm. The silicon substrate was an n-type silicon waferhaving 0.3 nm to 1.2 nm thick silicon oxide or silicon oxynitridecoating.

The AlN insulating interlayer was deposited atop the HfO₂ high-k gatedielectric by evaporating Al from a standard Al effusion cell that isresistively heated, and using a nitrogen beam from a commercial radiofrequency atomic nitrogen source. The effusion cell had a temperature of1000° C.-1200° C. during operation. The atomic nitrogen source wasoperated in the range of 200-450 W and a nitrogen flow rate of 1-3 sccm.The substrate temperature was kept between 150° C. to 650° C. duringdeposition. Base vacuum chamber pressure was about 5×10⁻¹⁰ to 2×10⁻⁹torr. During AlN deposition the pressure rose to the 1×10⁻⁵ ton range.The AlN layers were deposited to a thicknesses ranging from about 0.5 nmto about 2.0 nm.

A fully silicided NiSi metal layer (gate electrode layer) was thenformed atop the AlN insulating interlayer to a thickness ofapproximately 150 nm using chemical vapor deposition using standardprocedures. A polysilicon layer was first deposited atop the AlNinsulating interlayer. The polysilicon layer was then ion implanted withboron and the dopants activated by annealing following standardsemiconductor processing procedures.

A blanket Ni metal layer with a TiN diffusion barrier layer was thendeposited atop the polysilicon layer and a rapid thermal anneal in thetemperature range of 400° to 500° C. was employed to form NiSi. Theblanket Ni metal layer had a thickness on the order of about 70 nm andthe TiN diffusion barrier layer had a thickness on the order of about 20nm. A selective etch comprising H₂O₂:H₂SO₄ then removed the unreacted Niand the TiN layer. A second high temperature anneal on the order of 550°C. was then conducted to form the fully silicided NiSi metal gateelectrode.

Test capacitors 90 were then formed from the above structures usingchemical vapor deposition and etching to define pad shapes on the orderof about 50×50 square microns. Capacitors for comparative examplescomprising fully silicided NiSi metal gate electrodes on HfO₂ high-kgate dielectric 95 and fully silicided NiSi metal gate electrodes on anAlN insulating interlayer 85, as well as a control comprising fullysilicided NiSi metal gate electrodes on a SiO₂ gate dielectric 80, wereprovided using process steps similar to those used to form the testcapacitors 90.

The capacitors where then tested electrically to provide capacitance v.voltage plots. The flatband voltage (V_(fb)) in the capacitance voltagecurves for the capacitors is equivalent to threshold voltage (V_(t)) intransistors.

Referring to FIG. 8, flatband voltage (V_(fb)) measurements from thecapacitance v. voltage plots where then plotted versus the depositiontime for the AlN insulating interlayer. The flatband voltage (V_(fb)) ofthe SiO₂ control 80 is approximately 1.0 V. Comparison of the SiO₂control 80 to the HfO₂ comparative example 95 indicates that replacing atypical SiO₂ gate dielectric with a HfO₂ high-k gate dielectricdisadvantageously results in a shift of the flatband voltage (V_(fb)) toapproximately 0.4 V in devices comprising fully silicided NiSi metalgate electrodes. Comparison of the test capacitors 90, including an AlNinsulating interlayer, to the SiO₂ control 80 and the HfO₂ comparativeexample 95 indicates that the incorporation of the AlN insulatinginterlayer reduces the flat band voltage (V_(th)) shift by about 0.2 Vor more. The AlN comparative example 85 has a flatband voltage (V_(fb))that is closer to the flatband voltage (V_(fb)) of the SiO₂ control 80than the HfO₂ capacitors 95.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method of forming a semiconductor structure comprising the stepsof: providing a p-type semiconductor structure comprising at least onefirst patterned gate stack on a first channel portion of a substrate,said first channel portion separating silicided p-type source and drainportions of said substrate, said at least one first patterned gate stackcomprising a hafnium containing high-k gate dielectric atop saidsubstrate, an insulating interlayer atop said high-k gate dielectric,and a first fully silicided gate conductor atop said insulatinginterlayer, wherein the insulating interlayer comprises aluminum nitride(AlN), aluminum oxynitride (AlO_(x)N_(y)), boron nitride (BN), boronoxynitride (BO_(x)N_(y)), gallium nitride (GaN), gallium oxynitride(GaON) indium nitride (InN), indium oxynitride (InON) or combinationsthereof; providing an n-type semiconductor structure comprising at leastone second patterned gate stack on a second channel portion of asubstrate, said second channel portion separating silicided n-typesource and drain portions of said substrate, said at least one secondpatterned gate stack comprising the high-k gate dielectric atop saidsubstrate, and a second fully silicided gate conductor atop said high-kgate dielectric, wherein the insulating interlayer is not present; andbiasing said at least one first patterned gate stack and said at leastone second patterned gate stack, wherein said insulating interlayerstabilizes the p-type semiconductor structure's threshold voltage andflatband voltage to a targeted value without degrading the n-typesemiconductor structure's threshold voltage and flatband voltage.
 2. Themethod of claim 1 wherein said providing said at least one firstpatterned gate stack comprises depositing blanket layers of said high-kdielectric, said insulating interlayer, a polysilicon gate conductor anda dielectric cap atop said semiconductor substrate; and patterning saidblanket layers by lithography and etching.
 3. The method of claim 1wherein said insulating interlayer is formed by deposition or thermalgrowing.
 4. The method of claim 1 wherein said high-k dielectriccomprises HfO₂, hafnium silicate or hafnium silicon oxynitride.
 5. Themethod of claim 1 wherein said silicided p-type source and drainportions of said substrate are formed utilizing a first salicidationprocess.
 6. The method of claim 5 wherein said first salicidationprocess comprising forming at least one metal that can react withsilicon to form a metal silicide, first annealing to form a firstsilicide, selectively etching non-reacted metal, and optionallyperforming a second anneal that converts the first silicide into asilicide having its lowest resistivity phase.
 7. The method of claim 6wherein said first anneal is performed at a temperature from about 300°to about 600° C.
 8. The method of claim 6 wherein said optional secondanneal is performed at a temperature from about 600° to about 800° C. 9.The method of claim 1 wherein said dielectric cap is removed by anon-selective etching process.
 10. The method of claim 1 wherein saidfirst fully silicided gate conductor comprises NiSi or NiPtSi and saidsilicided p-type source and drain regions comprise CoSi₂.
 11. The methodof claim 1, wherein the insulating interlayer reduces said flatbandvoltage shift in the p-type semiconductor device by 0.2V or more whencompared to a similarly structured p-type semiconductor device includinga silicon oxide gate dielectric.